Coffee occurs predominantly as two species, Coffea Arabica (Arabica coffee) and Coffea Robusta (Robusta coffee). Beverages made from the two types have different flavour profiles. Robusta coffees are characterised as strong, earthy, bitter and neutral. Arabica coffees are characterised as mild, acidic and aromatic.
Green coffee contains a complex mixture of chemicals (principally chlorogenic acid, sugars, caffeine, trigonelline, proteins, amino acids and trace aroma compounds) which, on roasting, develop the flavour, aroma and colour typical of roasted coffee. Chemicals present in green coffee are precursors of roast coffee flavour and aroma.
Most green coffee (i.e. coffee cherries which have been processed to yield dry coffee beans) is processed simply by roasting. This develops the flavours, aromas and colour typical of the product. Prior to roasting, green coffee can be treated to remove caffeine (the so-called decaffeination process). In this process, beans are pre-moisturized and either put directly in contact with supercritical CO2 as a solvent to remove caffeine, or else the water-soluble proportion of the beans is extracted and the green extract is treated with activated charcoal to selectively remove caffeine. The caffeine-lean extract is then reinfused into untreated beans in a counter-current fashion. Such processes are for example described in U.S. Pat. No. 4,922,812, 5,147,674 or 5,208,056. There are other materials known with which caffeine can be removed from green extracts, such as carbon fibres, caffeine imprint polymers, fatty materials, zeolites, organic solvents, solvent systems, resins and others.
In addition to decaffeination, some green coffee is also treated prior to roasting by steaming at elevated temperature. This has the effect of reducing off-flavours in some coffees (notably Robusta coffees) and develops acidity. Steaming of green beans has been practiced by several companies for over 10 years, and used as a productivity technology because it enhances the quality of lower cost coffees, allowing substitution for higher cost coffees in blended products. The steaming process is for example described in U.S. Pat. No. 5,019,413. However, utilization of steamed coffee is limited because the process reduces some desirable coffee flavours and aromas (principally roasted notes) and introduces a processed note (indicated, among others, by β-damascenone and furfuryl pyrrole (FFP).
U.S. Patent Application Publication 2004/0081724 A1 describes a process for producing roasted coffee beans having reduced levels of acrylamide by reducing the level of asparagine in coffee beans comprising the addition of an asparagine-reducing enzyme to coffee beans.
Other U.S. patents describe the reduction or removal of further green coffee bean constituents from green extracts, however, these constituents are not flavour precursors and their reduction or removal is carried out for other reasons.
The removal of chlorogenic acid with resins is described in U.S. Pat. No. 4,031,251, with ligneous adsorbents in U.S. Pat. No. 4,160,042, with gel permeation chromatography on cross-linked modified polysaccharides in U.S. Pat. No. 4,872,987.
The removal of malic acid with ion exchange resins is described in U.S. Pat. Nos. 4,976,983 and 5,132,134 and by malolactic fermentation in U.S. Pat. No. 5,147,666.
The removal of potassium by ion exchange, membrane separation or electrodialysis is described in EP-0 534 024.
U.S. Pat. Nos. 4,278,696 and 4,317,841 describe the treatment of green extracts by deacidifying (increase of pH) with chitosan.
Treatment of roast and ground coffee extract with immobilized PVP or PVPP, in order to limit the aroma degradation of soluble coffee, is disclosed in EP 1 632 135 A1.
It is the object of the present invention to provide a process for modifying the flavour of Robusta and Arabica quality roasted coffee which overcomes the problems and disadvantages of the green bean steaming process, i.e. which does not reduce desirable coffee flavours and does not introduce a processed note.